Process for the treatment of hydrocarbon oils



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Marh 10, 1936. P. c. KEITH, JR

PROCESS FOR THE TREATMENT OF HYDROCARBON OIL Filed Feb. 8, 1934 ATTORNEYPatented Mar. l0, 1935 UNITED PATENT OFFICE PROCESS FOR THE TREATMENT OFHYDROCARBON OILS Percival C. Keith, Jr., Peapack, N. J., assigner toGasoline Products Company, Inc., Newark,

1 Claim.

This invention relates to processes for the treatment of hydrocarbonoils, and pertains more particularly to processes for producingrelatively light low boiling point oils such as gasoline from heavierhigher boiling point oils.

It is an object of my invention to provide an improved process forforming relatively light low boiling point oils such as gasoline fromheavy higher boiling point oils such as gas oil, crude oil, reducedcrude or the like, according to which novel interlocking heat exchangesteps are provided whereby highly efficient operation results.

In accordance with my invention fresh relatively heavy charging stock,such for example, as gas oil or other clean stock, or a relatively dirtystock such as crude or reduced crude, is passed in heat exchangerelation with condensate withdrawn from a fractionating Zone, then inindirect heat exchange relation with vapors 'withdrawn from a flashingoperatic-n, next in heat exchange with tar withdrawn from the hashingoperation, and is iinally introduced either into the fractionating zonementioned, or into an evaporating zone from which vapors pass to thefractionating Zone; reflux condensate is withdrawn from thefractionating zone, combined with distillate from the flashingoperation, and subjected to a cracking operation, the resulting crackedproducts being introduced into the evaporating zone, from which tar isdrawn off and introduced into the flashing Zone. According to anotherfeature of my invention, a portion of the composite charging stock isdiverted before passing to the cracking furnace and is passed inindirect heat exchange relation with liquid in the base of a stabilizingtower through which condensate, formed by condensing the fractionatedvapors, e. g. gasoline is passed. This charging stock is returned to thecracking furnace after passing through the indirect heat exchanger.

The above mentioned and further objects of my invention and the mannerof attaining them will be more fully explained in the followingdescription taken in conjunction with the accompanying drawing.

In the drawing the single gure represents diagrammatically an oilcracking system embodying my invention.

Referring more particularly to the drawing, reference numeral Iindicates a charging line through which fresh charging stock is forcedby -pump 2. The charging stock passes through indirect heat exchanger 2having control valve 65 and also through indirect heat exchanger 3,having control valve 4, and heat exchanger 5 having control valve 6,either through branch line 1 into evaporating section 8 of combinationevaporator fractionator tower II, or through branch line 9 intofractionating section Ill of the combination tower, or into bothsections simultaneously if desired. In case the fresh charging stock isa clean cracking stock such as gas oil or the like, the point ofintroduction of the charge may be at 9, in which case the charging stockwould be collected with the reflux condensate formed by thefractionating operation. However heavy dirty stock may be introducedthrough line 9 into the fractionating section I0 when it is not desiredto subject the composite liquid from the base of that section to a verydrastic cracking operation. The clean gas oil may also be introducedinto the evaporator section if desired, for cooling or any otherpurpose.

If relatively heavy dirty charging stock such as crude oil or reducedcrude is used, the point of introduction is preferably at 1, so that-the heavy dirty stock is subjected to a distilling operation in theevaporating section. Resulting vapors pass upwardly through the standpipe I2 into the fractionating section I0 wherein they I are subjectedto fractionation with the resulting formation of reflux condensate,which collects on the trap-out tray I3, while the unvaporized portion ofthe charging stock collects in the base of the evaporator section 8. Thereflux condensate collecting on trap-out tray I3 is removed through linei4 to accumulator or mixing tank I5, which is provided With a vent lineI6 for returning any vapors formed therein to the fractionating sectionI6 of the combination tower II. Composite cracking stock is removed fromthe mixing tank Iii through line I1 and forced by pump i8 through thecoils of cracking furnace or heater I9, wherein it is raised to acracking temperature and subjected to conversion. The i resulting hotproducts pass to reaction chamber 2@ wherein they are subjected toadditional conversion by their contained heat in the well known manner.The majority of the conversion may take place in the reaction chamber,or a part of L it may be effected in the cracking furnace and anotherpart in the reaction chamber. Alternatively the reaction chamber may beomitted if desired. The hot cracked products pass from4 reaction chamber28 through line ZI into the evaporating section 8 of the combinationtower EI, preferably below the liquid level therein.

The pressure in the evaporating section 8 is preferably keptconsiderably lower than that in the reaction chamber 20, for example byacyz Cil tion of pressure control valve 22. In the evaporating sectionthe introduced cracked products separate into vapors and liquid residue,the vapors passing upwardly through the tower around baiiie plates orsimilar devices 23, through stand pipe l2 and then upwardly through thefractionating section l0, wherein they undergo fractionation in the wellknown manner by contact with bubble trays or other similar fractionatingelements. The fractionated vapors, having the desired boilingcharacteristics, pass off from the top of the fractionating section,through line 24 and condenser 25, the resulting condensate beingcollected in gas separator 2E, having the usual gas draw-off line 21. Inthis gas separator xed gases separate from the liquid distillate, e. g.gasoline, this distillate passing through line 'I4 and pressure reducingvalve I5 into secondary gas separator 78, which is held under a stilllower pressure. In the secondary gas separator additional xed gases andlight vapors are separated and pass off through line 11, while theremaining liquid is removed through line 28 and forced by pump 29through heat exchanger 3U, wholly or in part, depending upon the settingof bypass valve 3l, into an intermediate point in stabilizer tower 32,through any one of the several branch lines 33. Fixed gases and lightvapors from the gas separator 26 may be passed through line 12, undercontrol of valve 73, into the base of flash tower 50 if desired, as willbe explained hereinafter. In this stabilizer tower, which preferablyoperates at considerably higher pressure than gas separator 16 theundesirably light constituents, including any xed gases present, areseparated from the final gasoline distillate, these light constituentspassing off from the top of the tower through line 34 and condenser 35,resulting condensate being collected in the reflux drum 35 from whichliquid is pumped back through line 3l as a refluxing medium, all of thisoperation being carried out in the well-known manner. The stabilizeddistillate collects in the base of the stabilizer tower and is withdrawnthrough lines 38, indirect heat exchanger 30, and cooler 39, to storage.Heat is supplied to the base of the stabilizer tower by withdrawing aquantity of liquid from a trap-out tray 4D located near the base of thetower, passing this through an indirect heat exchanger 4|, and returningthe resulting heated liquid to the base of the stabilizer tower throughline 42. Heat is supplied to the heat exchanger 4! by withdrawing aquantity of hot oil from the accumulator or mixing tank l5 and passingit through line 43 to the heat exchanger and back to the mixing tankthrough line 44, by action of pump 45. Reference numeral 46 indicates acontrol valve whereby a portion of the circulating liquid may beby-passed around the heat exchanger. Forty-seven (4l) indicates anothercontrol valve for regulating the amount of liquid being circulatedthrough the entire line.

Liquid residue collecting in the base of the evaporating section 8 ofcombination tow-er Il, is withdrawn through line 48 having thereinreducing valve 49 and is introduced into flash tower 50, which is heldat a pressure considerably lower than that maintained on the evaporatorsection 8. In this flash tower, as the result of the reduction inpressure, the lighter constituents of the residue are separated asvapors, and passed upwardly through the fiash tower undergoing partialfractionation by contact with baille plates or similar devices 5 I, andbubble trays or other fractionating elements 52. The vapors remaininguncondensed pass off the top of the ash tower through line 53, indirectheat exchanger 54, and indirect heat exchanger 3, wherein the vapors arepartially condensed, then through the final cooler or condenser 55, theresulting condensate being collected in receiving drum 56 which isprovided with the usual gas draw-off line 51. Flash distillate socollected is removed from the receiving drum and forced through line 58,under pressure generated by pump 59, a portion being returned to theflash tower 5 through valve line 88, as reiiuxing medium while anotherportion thereof passes through indirect heat exchanger 54, this latterportion in turn being sub-divided so that a part thereof passes throughvalved branch line 6| into the lower part of the fractionating sectionl0 as a refluxing medium, another portion passes through valved branchline 62 onto baiiie plate 23 in the evaporating section 8, while theremainder is directed through valved line 63 into the mixing tank l5, toform a portion of the composite charging stock for passage through thecracking furnace I9.

Additional separation or stripping of lighter constiutents from theliquid residue collecting in the base of the ash tower 50 may be insuredby passing fixed gases and light vapors from separator 26 through pipe12 into the liquid residue. The pressure of the separator 26 willordinarily be considerably higher than that of the ash tower so as tocause the ow of gas.

Reflux condensate is supplied to the top of the fractionator section ISby removing condensate from an upper tray in the fractionator section bymeans of line 64 and passing it through the indirect heat exchanger 2 inquantities controlled bythe adjustment of by-pass valve 65, andreturning the cooled liquid to the top of the fractionating column, thecirculation being effected by pump 65. The total amount of condensate socirculated may be controlled by valve 61.

When treating certain corrosive types of charging stocks it is desirableto add caustic or similar neutralizing agent to the stock as it ischarged to the process. This may be accomplished by the aid of branchline 68 through which a caustic solution withdrawn from supply tank 89is forced by pump 10, the quantity being controlled by valve 1l. Theamount of caustic so mixed with the fresh charging stock prior to itspassage through the cracking process depends upon the .corrosivecharacter of that charging stock, The ..f

greater the corrosive character of the stock, the more caustic solutionnecessary to effect neutralization. In general, it may be said that aquantity of the order of a few pounds of dry caustic per barrel ofcharging stock, will be suiiicient. The dry caustic may be rendered uidfor pumping purposes either by mixture with water or oil to form asolution, suspension or emulsion.

Operation In operation fresh charging stock, which may be either arelatively clean distillate charging stock such as gas oil, or arelatively dirty charging stock containing residual products such ascrude oil or reduced crude, is introduced through the line l and heatexchangers 2', 3 and 5, either into the evaporator section B orfractionator section I0 of combination tower Il, or may be introduced atboth levels. In the case ci a clean charging stock, the point ofintroduction would preferably be in the fractionating section lo, whilein the case of a dirty oil such as crude oil or reduced crude, the pointof introduction would preferably be in the evaporator section 8, when itis desired to operate the cracking furnace I9 at relatively highcracking per pass. On the other hand, even the heavy dirty oil might becharged to the fractionator section IIB if the cracking per pass in thefurnace I9 be kept low enough to prevent deleterious coke formation. Analternative method of operation would be to introduce quantities of thecharging stock into both the evaporator and into the fractionator.

The fresh charging stock in the combination tower is heated by risinghot cracked vapors and subjecting to partial vaporization, the vaporspassing upwardly through the fractionating tower and the fractionatedvapors, having the desired boiling characteristics, being removedthrough the vapor line 24 and condenser 25 and the resulting distillatebeing collected in the primary gas separator 26. In this gas separatora` quantity of fixed gases and light vapors are separated and pass offthrough line 21 or through line 12, leaving liquid oil which travelsthrough pipe 14 and reducing valve 15 into the secondary gas separatorwhich is held under substantially lower pressure and wherein additio-nalfixed gases and light vapors separate. The xed gases and light vaporspass off through line 11 and the remaining distillate is pumped intostabilizer tower 32 after being preheated in heat exchanger 36.

Reiiux condensate from the fractionating operation, together with anyunvaporized portions of the fresh charging stock, if that be introducedthrough pipe 9, is withdrawn through line I4 to the accumulator tank I5,from which it is removed and passed through the cracking furnace I9 andreaction chamber 20 to cause any desired amount of cracking thereof.'I'he cracking in the furnace I9 and reaction chamber 26 is preferablycarried out at a pressure of several hundred pounds per square inch, forexample, about 700 or 800 pounds per square inch and at a temperaturesuiiicient to cause the desired conversion per passage of the oilthrough the cracking apparatus. This amount of conversion would, ofcourse, be dependent upon the coking tendency of the stock charged tothe furnace. A relatively clean stock such as the gas oil and refluxcondensate from the fractionating operation could be subjected to ahigher temperature than a stock containing residual components, such asreduced crude. In general, it may be said that the temperature may rangefrom 850 to 950 F., an average value for clean stock being about 925 F.In the combination tower, to the evaporating section 8 of whichthecracked products pass through line 2I, a pressure considerably lowerthan that in the cracking furnace and reaction chamber is most desirablymaintained.v The control of this pressure is effected by means ofpressure reducing valve 22. 'Ihe pressure in the evaporating section maybe, for example, about 150 pounds per square inch and that of theprimary gas separator 26 may be about the same value, while thesecondary gas separator 16 is held under a considerably lower pressuresuch as 30 pounds per square inch. The pressure on the stabilizer 32 ispreferably higher, for example, 250 pounds per square inch. In theevaporating section separation of the introduced cracked products intovapors and liquid residue takes place, the vapors rising upwardlythrough the tower past the baflie plates or similar devices 23 andthrough the fractionating section I0, wherein it undergoes fractionationin the manner set forth hereinbefore.

The liquid residue collects in the base of the evaporating section andis passed through line 48, having reducing valve 49 into flash tower 50,which is held under a still lower pressure, for example about pounds persquare inch. In this fiash tower separation of vapors fromliquid residuetakes place by the contained heat of the introduced residue, as well asby action of fixed gases and light vapors from gas separator 26, whichare introduced in desired quantities through line 12. The vapors passupwardly through the flash tower, undergoing partial fractionation andthe vapors remaining uncondensed at the top of the tower pass throughthe heat exchangers 54 and 3, giving up heat to the flash distillate andfresh charge respectively, then through condenser 55, the resultingcondensate being collected in the accumulator tank 56. The liquidresidue remaining in the base of the flash tower is withdrawn, forexample, as fuel oil through line 18 under control of valve 19. Thelighter fractions which tend to remain in the liquid residue may beremoved by injecting fixed gases and light vapors, from gas separator26, into the residue by way of line 12, the quantity being controlled byvalve 13. Distillate is removed from the receiving drum 56 and pumpedback to the top of the flash tower through line 66 in quantitiesnecessary to assure the desired characteristics of the vapors leavingthat tower, while other portions of the distillate pass through heatexchanger 54 and thereafter may be introduced either into thefractionating section Ill or evaporating section 8, of the combinationevaporating and fractionating tower II, or may be introduced into themixing tank or accumulator l5, or it may be introduced into all of theseseveral places simultaneously. The quantity introduced into theevaporator tower is preferably only sufcient for reiiuxing purposes,while the remainder is diverted either through the line 6I into thelower part of the fractionating column or into the mixing tank I5. Wherethe quantity of distillate available is relatively large it would bemore suitable to introduce only part of this distillate through the line6I so as not to interfere with the eiiiciency of the fractionatingoperation, the rest being passed directly to the mixing tank I5 for`cracking in the furnace I9.

A part of the composite stock is removed from the accumulator I5 andpassed through the heat exchanger 4I wherein the contained heat is usedfor reboiling condensate collected in the stabilizer tower 32, thecomposite stock being thereafter returned to the mixing tank. It hasbeen proposed heretofore to remove reflux condensate from thefractionating column and utilize it for reboiling the stabilizerbottoms, the cool stock being returned to the fractionating column, butthe present operation of utilizing stock from the mixing tank I5 has theadvantage over the process just mentioned of avoiding any disturbance tothe fractionating operation. The condensate removed from the stabilizertower and passed through the heat exchanger coil 4I is preferablywithdrawn from a trap-out tray such as 4B, and returned, after beingheated, above the level of the liquid in the base of the stabilizertower, this operation resulting in heating the removed condensate andseparating lighter fractions therefrom as vapors before the returnedstock is commingled with the liquid collected in the base of thestabilizer tower.

The caustic, which may be introduced with the fresh charging stockthrough line 68, is preferably injected in the form of a slurry ofcaustic with Water or oil, the amount of caustic so introducedpreferably being only a small percentage of the amount of chargingstock. The exact amount introduced would of course depend upon thecorrosive character of the charging stock, some stocks requiring only aVery little caustic, whereas others might require many times as much. Ingeneral it may be said that not more than a few pounds of caustic perbarrel of charging stock need ordinarily be used.

While I have described a particular embodiment of my invention for thepurposes of illustration it should be understood that variousmodications and adaptations thereof may be made Within the spirit of theinvention as set forth in the appended claim.

I claim:

The process of treating hydrocarbon oil which comprises passing chargingstock through a cracking zone wherein it is raised to a crackingtemperature and subjected to conversion, introducing the resultingcracked products into an evaporating zone wherein vapors separate fromliquid residue, removing vapors from said evaporating zone and passingthem to a fractionating zone wherein fractional condensation thereofoccurs, removing fractionated vapors from said fractionating zone andcondensing them as a desired product, removing liquid residue from saidevaporating zone and subjecting it to reduced pressure in a ashing zone,removing vapors from said ashing zone and condensing them, removingunvaporized products from said flashing zone, transferring heat from hotvapors near the top of said fractionating zone to cooler fresh chargingstock so as to provide reiiux for said fractionating zone and heat saidcharging stock, passing the resulting partially heated charging stock inindirect heat exchange with hot vapors removed from said flashing zone,then in indirect heat exchange with unvaporized liquid removed from saidashing zone and iinally introducing the preheated fresh charging stockinto direct contact with vapors separated from the hot cracked productsintroduced into the evaporating zone, condensing vapors removed fromsaid flashing zone subsequently to the passage thereof in indirect heatexchange with said fresh charging stock, passing resulting condensate inindirect heat exchange with vapors removed from said ashing zone priorto the passage of said vapors in indirect heat exchange With saidcharging stock and then introducing the heated condensate into directcountercurrent contact with vapors separated from the hot crackedproducts introduced into the evaporating zone.

PERCIVAL C. KEITH, JR.

